Suspension coating of filaments



United States Patent 3,278,329 SUSPENSION COATING 0F FILAMENTS Sol B.Wiczer, 1815 H Stu NW., Washington, D.C. No Drawing. Filed Dec. 6, 1961,Ser. No. 157,591 4 Claims. (Cl. 117-62) This invention is acontinuation-in-part of my copending applications, Serial Number353,003, filed May 4, 1953, now Patent Number 2,862,684, issued December2, 1958; Serial Number 777,344, filed December 1, 1958, now abandoned.

This invention relates to fiber modified by a coating upon the fiber toproduce therein surface irregularity by coating the fiber with a.plastic substance containing a gasforming agent, and then treating thecoated filament to activate the gas-forming agent to impart an irregularbubbly character to the surface of the filament to impart improvedsurface characteristics before spinning into a yarn or weaving into afabric; or the coated filament before or after coating may be choppedinto short lengths and then confined in a mold and treated to activatethe gas-forming agent in the surface coating to form a porous moldedproduct having a filamentaceous filler; and to the methods of formingthese products.

According to the present invention, the synthetic plastic filament iscoated with a composition having incorporated therein a gas-formingagent to acquire after generation of the gas a foamy texture, and mostdesirably, for purposes hereof, a texture wherein the surface has aseries of pores formed by the expansion of gases therefrom during astage of formation wherein plastic coating material is sufiicientlypliable to be slightly deformed by expansion of the gas, butsufiiciently set in the filament form to avoid destruction of itsfilamentary character. As this invention is preferably practiced, anagent, herein, called a blowing agent, comprising an unstable compoundcapable of developing a gas by decomposition, as by application of heator by reaction with subsequently applied reagent, is associated withplastic material after being formed into filament and coated to impartthereto by expansion of the gas the desired porous surfacecharacteristics hereof.

In another aspect of this invention, a relatively heat stable finefilament core of natural or synthetic fiber is formed with athermoplastic coating composition containing a blowing agent or agas-evolving substance capable upon heating and expanding only theheated and softened coating composition to a porous form withoutaffecting the filamentaceous core upon which it is coated. Thethermoplastic coated filament may have the blowing agent incorporated atany of several stages of its production. The coated filament core,usually available in con tinuous lengths, may he coated with athermoplastic film-forming substance, for example polystyrene dissolvedin a solvent which can contain a blowing agent, or the gas-evolvingproperties can be imparted to the filament after coating with thethermoplastic film. The coated continuous filament lengths containingblowing or gasevolving agents are then chopped into short lengthsranging approximately from about A" to /4 In still another alternateprocedure, the filament core may first be chopped into such shortlengths and then coated with the thermoplastic coating compositioneither containing the blowing agent using a sufiicient heat or a solventto fiuidize the coating for application to the filament core butinsufiicient to activate the blowing agent, or the thermoplastic coatedshort lengths of filament can have the blowing agent or gas-formingproperties imparted in a subsequent treatment stage after the filamentshave been coated.

In still another alternate form, the chopped short fila- 3,278,329Patented Oct. 11, 1966 "ice ment lengths can be dipped in a liquidmonomer or solution of preformed polymer in monomer, and thepolymerization of the monomer may then be completed in situ as a coatingupon the filament. For instance, in a perferred procedure, the monomercoated short filament lengths may be suspended by agitation in a waterbath and dispersed as individual filament together with catalyst andsuspending agents until the polymerization is completed as athermoplastic coating upon each individual filament core material. Thechopped short thermoplastic polymer coated filament lengths may finallybe treated to impart blowing or gas-forming characteristics thereto; oralternately, the monomer or monomer solu tion may have dissolved orsuspended therein a blowing agent which will not affect thepolymerization of the monomer and will remain inactive while the monomeris being polymerized in situ upon the filament core materials coatedtherewith. Thus despite the application of necessary heating of theagitated suspension in water at a temperature to complete thepolymerization as a coating upon each filament, the temperature isinadequate to activate the blowing agent. Whichever procedure isfollowed, short chopped lengths of thermally stable filament core havinga coating of thermoplastic polymer substance containing a blowing agentis produced as fine free-flowing filamentaceous particles containing ablowing agent. In use such thermoplastic expandible filament particlesare loaded to partially fill a mold, and the closed mold is then heatedsufficiently to activate the gas release to cause expansion of thethermoplastic coating by simultaneous heat softening and release of thegas from the blowing agent with the heat, the expansion of each coatingfilm upon the filaments fills the mold and shapes the product accordingto the form of the mold developing sufficient pressure and softening ofthe thermoplastic to cause cohesion to a monolithic molded product. Suchproduct, while having the light porosity of an expanded plastic molding,has the great strength of well distributed and well bondedfilamentaceous filler throughout the product.

The specific handling procedure for developing the gas and consequentsurface porosity in the filament will vary slightly with organic plasticmaterials from which the filament is formed depending upon specificphysical and chemical characteristics of the plastic material.

Where the filament is a thermoplastic material it may be linearsuperpolyamide such as nylon, linear polyester such as polyethyleneterephthalate, polyacrylonitrile, styrene or polymerized solutions ofpolymer in a monomer of such substances, or other thermoplasticmaterials, or it may be of inorganic plastic such as silicone polymer oreven glass, capable of extrusion into filaments by fluidizing theplastic with heat and setting the filament by cooling. The gas blowingagent may be suspended in the same or a different plastic coatingcomposition and coated upon the filament and thereafter the filament isgiven a heat treatment sutficient to decompose the blowing agent in thecoating without destroying the filamentaceous character of the filament.In such process the blowing agent, such as an azo compound, will beselected to decompose at a temperature below that at which the plasticis substantially molten, i.e. at a temperature wherein the plastic ismerely soft.

In another alternative procedure, particularly useful where the plasticmaterial is chemically set by chemical reaction with the bath such as incellulose base plastics such as viscose, cellulose xanthate andcellulose esters, the spinning solution comprising the cellulose plastichas incorporated a gas-forming agent and the gas is developed bychemical reaction with the 'bath. For this purpose, a cellulose solutionsuch as alkali cellulose has incorporated a gas-forming salt like sodiumcarbonate, and the cellulose solution is then coated upon the filamentwhich is then passed into an aqueous acid bath which serves the dualpurpose of both regenerating the cellulose and causing the gas to beformed by reaction with the sodium carbonate to evolve carbon dioxideand produce a bubbled surface texture.

In still another procedure where the filament is set by a chemicalcoagulation bath, as usually used for cellulose filaments, the coatedfilament, such as coated glass fiber, while still swollen and gelatinousprior to drying, may have the gas-forming agent dusted thereon which maybe either acid reactive, i.e. reactive with the acid solution clingingto the swollen filament from the coagulating bath, such as by dustingsodium carbonate on the acid wet cellulose coated filament, or, sincecellulose filaments are thermally stable at substantially raisedtemperatures, the blowing agent dusted upon the swollen coated filamentmay be such as is activated by heat, and may be dusted upon the wetswollen filament to adhere directly thereto. The filament thereafter, ascoated with the dusted blowing agent, may be passed through a heatedtube to raise the temperature sufficient to cause evolution of gas fromthe blowing agent and simultaneously to dry the same.

As a slight modification of the last procedure, useful where thefilament is formed of thermoplastic material, the thermoplastic filamentmay be passed through a bath containing an organic liquid such as aplasticizer liquid or a liquid which is more volatile, where a residualplasticizer coating is not desirable, and which liquid has the effectmerely to swell and soften the surface of the filament. Simultaneouslythe plasticizer or swelling liquid may contain the blowing agentdissolved or dispersed therein and thereby serves not only to swell thefilament but to impregnate the same with blowing agent, Thereafter, theswollen thermoplastic filament is heated sufficient to evaporate thesolvent and develop the gas from the blowing agent but insufficient tomelt the filament and destroy its thermoplastic character. For example,a thermoplastic filament such as linear polyamide, polyester, orpolyacrylonitrile, etc., is first extruded through a spinneret and isthen passed through a bath comprising a solution of dimethyl formamideand water having dissolved therein 3% of a blowing agent. The blowingagent may be heat activatable at a temperature below the fusing point ofthe filament material. Or the blowing agent may be activatable by acidsuch as sodium carbonate. The filament thus coated is dried and may bepassed through a hot tube at a temperature merely high enough toactivate the blowing agent without melting the filament material.Alternatively, the coated filament, if coated with sodium carbonate, maybe passed through a dilute aqueous bath of hydrochloric acid.

The 'bath material may contain a film-forming binder substance whichserves to bind the blowing agent to the surface of the filament in athin film coated thereover. Thus, for example, an extruded nylon orother thermoplastic filament may be passed through a bath containing adilute solution of viscose, cellulose xanthate, etc., which furthercontains dissolved therein sodium carbonate. The filament is then driedwith warm air and then passed through a bath which contains acidcoagulating agents which serve both to regenerate the cellulose in thefilm and activate the sodium carbonate to develop gas bubbles in thesurface.

In a further modification a heat stable core material as filament, suchas relatively heat stable cellulosic filament; for example, cotton,rayon or acetate fiber, other heat stable filaments such as silk, wool,glass, silicone, Orlon, Dacron or nylon fiber or the like iscontinuously dipped in a solution of styrene monomer containing rubber,and the wet coated filament is heated by passing continuous lengthsthrough a hot tube until the polymerization is completed. The styrenemonomer may contain an oxidizing catalyst as benzoyl peroxide toaccelerate the polymerization. Thereafter, the filament coated withpolystyrene is heated with a petroleum solvent such as petroleum etherhaving 4 to 7 carbon atoms boiling in the range of about 30 to C. orother easily gasified solvent or softening agent such as methylenechloride, methyl chloride, acetone or the like, which swells and softensthe thermoplastic polystyrene coating upon the fiber Without dissolvingit. Thereafter, the fiber which may then be first precut into shortlengths before treatment with the swelling agent or may be cut intoshort fiber lengths, and after having been treated with the swellingagent, is used as a filamentaceous molding powder as described.

In a further alternate procedure, short lengths of a fiber core materialwhich are relatively thermally stable at temperatures below a practicalrange of to 200 C., are chopped into short lengths coated with liquidpolymerizable monomer such as styrene, acrylonitrile, methylmethacrylate, vinyl chloride, vinylidenechloride, vinyl acetate,butadiene, 2-ch'lorobutadiene, dicyclopentadiene and the like, whichmonomer may contain a polymer dissolved therein, such as GRS rubber,butyl rubber, neoprene and the like, in quantity up to about 30 to 40%.Such monomers and solutions of preformed rubbers therein uponpolymerization form coatings such as polystyrene, polyurethane,polyacrylonitrile, polybutadiene, polycyclopentadiene, poly2-chlorobutadiene copolymers of styrene and butadiene and polymerizedsolutions of copolymers of butadiene and styrene, polybutadiene,polycyclopentadiene, polyvinyl chloride, polyvinylidene chloride andcopolymers of polyvinyl chloride-polyvinyl acetate copolymer in amonomer of said polymers. Other monomers or liquid mixtures capable ofpolymerizing such as diisocyanate-phthalic a nhydride or maleicanhydridc, epoxy mixtures such as 2,2-diphenylol propane andepichlorohydrin or hydroxy acetone and formaldehyde and the like, may becoated upon the fiber and then polymerized thereon.

The monomer may further contain a small quantity of a wetting agent suchas sodium dodecyl benzene sulfonate or equivalent wetting agent inquantity of about 0.001% to about 0.1% by weight of water insolublemonomer and the wet coated fibers in short chopped lengths can besuspended with agitation in water containing a suspending agent, such asfine particles of calcium phosphate, polyvinyl alcohol or the like, andthe suspension can then be heated with agitation until thepolymerization is completed as a coating in situ upon the fiber core.

Thereafter, the coated short fiber lengths are treated with gas-evolvingagent such as a vaporizable solvent such as butane, pentane, hexane, orpetroleum ether mixture until the coating swells. After superficialdrying to remove surface solvent, the coated, empirically dry fibers arepackaged for subsequent use.

Thereafter, in use, upon partially filling a mold and heating to athermo softening temperature the occluded propane in the coating puffsup the softened coating softened sufficient to allow release of thepentanc, and foaming of the coating into a porous tacky mass results. Asconfined in a mold, the fibrous product fills the mold and integrallyfuses to a monolithic molded mass. This produces a very strong moldedmass in which the short fibrous core materials remain as a strongreenforcing filler substance intimately adhered to the porousthermoplastic coating thereon. Moreover, as the mold is filled and thesoftened foamed plastic is reenforced with the numerous well distributedshort fiber lengths, there is no substantial tendency of the mass tocollapse or shrink after the heating is discontinued.

The quantity of gas blowing agent contained in a filament coatingcomposition is usually held to less than about 3% as a maximum, variableslightly with the quantity of gas that may be evolved by the particularchemical, but the quantity of such is usually held to between .5% and1.5% of the weight of thermoplastic type plastic with which it isincorporated.

Suitable blowing agents for use herein where they are organic areusually diazo compounds and many are known in the art as gas developersactivatable for this purpose over a wide range of temperatures andaccordingly one is readily selected to evolve gas at the desiredtemperature. Typical examples are:

Phenylazo ethyl sulfone Phenylazo isopropyl sulfone Phenylazo n butylsulfone p-Xenylazo ethyl sulfone p-Chlorophenylazo-ethyl sulfone pChlorophenylazo-methyl sulfone p-Tolylazo-methyl sulfone Phenylazmmethylsulfone 2,5-dichlorophenylazo-methyl sulfone Phenylazo p-t-olyl sulfonep-Tolylazo phenyl sulfone p-Chlorop'henylazo-p-to-lyl sulfonep-Chlorophenylazo phenyl sulfone p-Chlorophenylazo-p-chlorophenylsulfone 2,S-dichlorophenylazo-phenyl sulfone Phenylazo-p-chlorophenylsul-fone p-Tolylazo-p-chlorophenyl sulfone p-Tolylazo-p-tolyl sulfoneBiphenylazo-p-tolyl sulfone Diphenyl bis(az-ophenyl sulfone)-4,4'Di-p-tolyl bis(azophenyl sulfone)-4,4

These blowing agents decompose to evolve gas when heated to atemperature in the range of 80 to 200 C. For example, parachloro phenylazo methyl sulfone would evolve gas when heated to 115 to 118 C. Othertypes of azo compounds are useful, for example, diazo amino benzene,alpha,alpha-azo-bis-isobutyrontrile, various triazenes such as1,3-b-is(O-xenyl)-triazene which develop gas when heated at 130-135 C.and various members of this group decompose to develop gas attemperatures variable over the range of 115-140 C. For the chemicalreactive type of gas-evolving agent in addition to the sodium carbonatementioned above, other inorganic carbonates may be used.

The organic type blowing agent is generally soluble in the organicplastic and the sodium carbonate would be soluble in the aqueous mediumof the alkaline ripened cellulose or xanthate thereof, but the blowingagent may be incorporated as a dry insoluble powder in the plasticprovided that it is sufficiently finely divided to pass through thespinneret openings and for this purpose would be reduced to a particlesize of extreme fineness of about the order of 1 or 2 microns or less.The following examples illustrate the practice of this invention:

Example I Polyethylene terephtha-late having a molecular weight of about65,000 is melt extruded to a filament, cooled in air to normal roomtemperature and then passed through a bath containing a viscose solutionas described in Example 5 comprising originally about 6.5% of sodiumhydroxide and 8% of cellulose, 4% of sodium carbonate and 1% of sodiumlauryl sulfate as a wetting agent. The extruded filament is passedthrough this bath to pick up a coating of viscose thereover and then ledinto a second bath comprising the coagulating bath of Example 5. Thefilament is found to have a fine porous coating of regeneratedcellulose.

Example II Polyethlene terephthalate after melt extrusion into filament,and cooled to set the filament at ambient room temperature, is heated bypassing the filament through a tube maintained at a temperature of 150C. The filament is then passed through a pair of cold polished stainlesssteel tangential rollers on which powdered parachlorophenyl azomethylsulfone was added by dusting on the rollers and the powder pressed bythe tangential roll into the surface of the soft filament while coolingthe same. The filament is again reheated to a temperature of 160 C. todecompose the gas evolving azo compound impregnated in the surfacethe-reof. Thereafter the filament may be stretched, crimped, treatedwith p-lasticizing fluids, etc. as desired and the filament will befound under microscopic examination to have a series of peck-marks andsurface pores caused by the decomposition of the powdered blowing agentadhered thereto.

Example III Continuous filaments of fiber glass are passed through a 20weight percent solution of polyacrylonitrile of about 60,000 M.W. indimethylformamide having 2% of diazoaminobenzene added thereto. Thefilaments after coating are dried in warm air at C. and then passedcontinuously through a heated tube at C. to decompose the blowing agentand form a bubbly surface. Multifilament yarns spun of these filamentshave the usual strength in tension of fiber glass, but have considerablyincreased strength in shear as well as much enhanced insulating value,low heat transfer, .as compared to untreated glass fiber thread andfabric woven therefrom.

In a slight modification of this example, after the coated filament isdried in warm air, it is cut into short lengths ranging from /s to /1.",generally averaging about A, and packaged as such for subsequent use. Inuse, the coated glass filament is loaded into a mold, partially fillingthe same. After the mold is closed, it is heated to about 200 0, therebydecomposing the blowing agent and softening the coating until it istacky. The coatings upon the filament expand, causing the entire mold tobe filled with a well distributed mixture of short filaments, and theexpanded coatings cohere into a monolithic molded body of high porosityand great strength, Well reenforced by the fiber. A molding such as /2thick flooring placque may be formed which is highly resilient but hasvery good wearing strength.

In a further modified procedure, the mold, as described in the precedingparagraph, can be formed by placing a closure such as an invertedrectangular form upon a flat surface, such as an intermediate flooringbase of cement or wood, which may have been coated with mastic. The moldis partly filled as before with evenly distributed coated glass fiberand the mold assembled upon the floor is heated to form the rectangularfloor placque so that, upon cooling, the molded plate upon the floor isan expanded porous tile placque having substantial resiliency, even asformed in situ as flooring upon the floor. In this manner, a completeflooring may be applied placque by placque to mold flooring in situ, theflooring having great strength and substantial resiliency.

Example IV Polyhexamethylene adipamide has incorporated thereinapproximately 1% of sodium carbonate as fine powder milled to an averageparticle size of about 1 micron. It is melted and extruded through aspinneret and hardened as a multi-filament batch in air and then passedthrough a tube through which is led wet steam at 100 C. containing 5% ofhydrochloric acid gas, then led through a neutralizing bath containing.5% of sodium carbonate at a pH of about 8 and finally through a coldwater washing bath and finally through a warm air drying tube. Thefilament is found to be surface porous dotted with tiny depressions.

Example V A viscose coating solution containing about 6.5% of sodiumhydroxide and 8% cellulose prepared in the conventional manner is madeafter ripening to an index of about 4 (sodium chloride) with 1% ofsodium carbonate homogeneously dissolved therein. Glass fiber iscontinuously passed through this voscose solution and the wet coatedglass filaments are then passed directly into a bath containing about12% of sulfuric acid, 22% sodium sulfate, 1.5% of zinc sulfate and atrace of a wetting agent. Thereafter the filaments are dried to producea porous surfaced strong fiber as in Example 4.

Example VI In an alternate procedure, polyacrylonitrile of molecularweight of about 60,000 after soaking in water and damp pressing is mixedwith 3% of parachlorophenyl azo-phenyl sulfone in the form of finepowdered particles and then extruded as a filament under a pressure ofabout 2,000 p.s.i. and a temperature of 140 C. from a 35 mm. spinneret.It is then cooled to room temperature in air and passed through theviscose bath having the composition as described in Example to which noadditional blowing agent was added. Thereafter, the viscose coatedfilament was passed through a coagulating bath as described in Example5. Finally the filament Was heated to 175 C. by passing through a heatedtube. The filament was found to be porous throughout and substantiallyexpanded.

As thus described, filaments are produced which have a porous texture.In this instance of using glass fiber as the core material, the filamentis of great strength. The desirable characteristics are further impartedby the surface coating which alone may be porous. That surface materialof organic plastic may also impart substantial strength to the fiber asillustrated in the following example.

Example VII Glass fiber is passed as continuous filament through aweight percent solution of poly phenol siloxane having a molecularweight of about 40,000 dissolved in n-heptane and further containing1.5% of phenyl azo-methylsulfone, dried in air at 100 C. and immediatelypassed through a heated tube at a temperature of 260 C. to developsurface pores.

In a slight modification of this example, the coated fiber after dryingis chopped into short lengths ranging from about A; to A", and usuallypackaged for subsequent use. When used, it is placed in a mold, onlypartially filling the mold, and the closed mold is then heated to causeexpansion of the silicone coating by activation of the blowing agent ata temperature of about 260 C. That temperature also softens the residualsilicone coating making it tacky and bringing it by expansion intocontact with expanded surfaces of several other neighboring filamentswhich are all caused to cohere by contact of the softened silicone intoa monolithic molding, which upon cooling of the mold fully retains itsshape, porosity, and substantial strength.

Thus a filament surface is modified to impart tiny pores or semicircularholes comprising a surface irregularity. Yarns or bats formed from suchfilament tend to occlude greater quantities of gases and thereby have ahigh insulating effect. They are, moreover, more amenable to felting.

Example VIItI Glass fibers are chopped into short lengths and are wetwith monomeric styrene, centrifuged or drained to remove excess liquidstyrene, and are then placed in a continuously agitated water bath ofabout equal quantities; that is, 100 parts of water to about 100 partsby weight of wet coated fiber. Before coating, the styrene had added tothe bath 100 parts of styrene monomer, 0.05 part of dodecyl mercaptanmodifier, 0.2 part of antioxidant and 0.08 part of benzoyl peroxide. Thewater bath has added thereto per 100 parts, 0.6 part of trisodiumphosphate, 0.78 part of calcium chloride, 3.0 parts of polyvinylalcohol, 0.0036 part of lecithin and 0.12 part of anionic emulsifyingagent comprising dodecylbenzene sodium sulfonate. The suspension isstirred with heating for a period of about 6 hours, the temperature riseamounting to about 100 C. and maintained until the styrene haspolymerized to a hard coating. Thereafter, the coated fiber is removedfrom the bath, washed, centrifuged to remove water and dried in air. Thecoated fiber is then dipped in petroleum ether boiling from 40 to 60 C.until it is swollen. It is then placed in a mold, partially filling thesame, and the closed mold is heated to cause expansion of the styrenecoating which swells to form a foam and each coated fiber coheres to theothers forming a monolithic product of the shape of the mold, as anintegrally strong monolithic form, while being light and highly porous.

Following the procedure of this example, the fibrous base substance maybe varied by substituting for the glass fiber such other fibrous bodiesas wool, cotton, or glass, or some synthetics which are comparativelyinsoluble and heat stable at temperature above about 100 C. such ascellulose esters and ethers, for instance cellulose acetate fiber,polyacrylonitrile fiber such as Orlon, polyterephthalic ethylene glycolcondensate and mixed acrylic fibers such as Dynel or Chemstrand,polyamid fibers such as nylon or other fibers.

Example IX Chopped cotton fiber lengths are wet with monomeric styrenehaving dissolved therein 25% of GRS rubber. The coated fiber is treatedexactly as in Example 8 to set the coating to a high impact polymercoating on the fiber. It is then treated to impart gas-forming agent bysoaking in petroleum ether, the coated fiber being ultimately expandedin a mold to form a high impact strength highly porous molding greatlyreinforced by the integrally coated and cast fibrous core materialcontent.

Example X Continuous lengths of glass filament are run through a moltenbath comprising parts of polystyrene, 3 parts of methyl chloride and 2parts of tetrachloro ethane. The coated glass fiber is cooled and thenchopped into short lengths. The chopped fiber is then soaked in apartial solvent such as acetone until it is substantially swollen. It isthen partially dried in a vacuum and packaged for subsequent ready use.The empirically dried packaged fiber is used by partially filling a moldand then heating to cause the solvent acetone to expand so that eachcoating coheres to the next, filling the mold by expanded coatingsbonded to fiber core to form a strong monolithic molded mass of highstrength and porosity. The molded product is found to be fire retardentand will not support combustion. Various swelling agents may besubstituted for the acetone; for instance, methylene chloride, methylchloride, n-pentane, n-butane, isobutane, isopentane, neopentane and thelike.

I claim:

1. A process of forming short filaments expandable into a strongcoherent molded ifoamed body comprising coating short lengths of waterinsoluble heat stable filaments with a water insoluble liquid monomerpolymerizable into a thermoplastic film, suspending the wet monomercoated filaments in water and agitating with heat to effectpolymerization of the coating upon individual filaments in suspension,removing the thermoplastic polymer coated short lengths of filamentsfrom the water suspension and impregnating the thermoplastic coatingwith a gas-forming agent adapted by heating of said thermoplasticcoating to its tacky softening point to be converted to fine gaseousbubbles in the coating, thereby expanding the softened coating to acoherent foam.

2. The process of coating fiber with polymer comprising wetting thefiber with a water insoluble polymerizable monomer liquid, suspendingthe said monomer-coated fiiber in water containing suspending agents andagitating with heat for a period sufficient to effect polymerization ofthe coating upon the individual fibers, removing the References Cited bythe Examiner UNITED STATES PATENTS 1,829,906 11/1931 Lilienfeld 117-166X 2,125,827 8/1938 Turkington 117-119.8

Neville et a1.

Soday 117-140 Church 260-8 Elliott 260-25 X Kropa et al 260-25 X Biefeldet a1. 117-1355 Weil et al 260-25 X Swann 117-4 Wiczer 260-25 X Bradt117-4 X Muskat et al 264-43 Daly 260-415 WILLIAM D. MARTIN, PrimaryExaminer. 15 R. HUSACK, Examiner.

1. A PROCESS OF FORMING SHORT FILAMENTS EXPANDABLE ING A STRONG COHENENTMOLDED FOAMED BODY COMPRISING COATING SHORT LENGTHS OF WATER INSOLUBLEHEAT STABLE FILAMENTS WITH A WATER INSOLUBLE LIQUID MONOMERPOLYMERIZABLE INTO A THERMOPLASTIC FILM, SUSPENDING THE WET MONOMERCOATED FILAMENTS IN ATER AND AGITATING WITH HEAT TO EFFECTPOLYMERIZATION OF THE COATING UPON INDIVIDUAL FILAMENTS IN SUSPENSION,REMOVEING THE THEROMOPLASTIC POLYMER COATED SHORTER LRNGTHS OF FILAMENTSFROM THE WATER SUSPENSION AND IMPREGNATING THE THEREMOPLASTIC COATINGWITH A GAS-FORMING AGENT ADAPTED BY HEATING OF THERMOPLASTIC COATING TOITS TACKY SOFTENING POINT TO BY CONVERTED TO FINE GASEOUS BUBBLES IN THECOATING, THEREBY EXPANDING THE SOFTENED COATING TO A COHERENT FORM.